Radio frequency generator including pulse generator circuit to provide complex RF pulse pattern

ABSTRACT

A radio frequency (RF) generator includes a pulse generator circuit configured to receive input signals indicative of a pulse pattern comprising pulse segments, the input signals defining power levels and durations for the pulse segments. The pulse generator circuit generates a pulse modulation control signal for each pulse segment responsive to the input signals. The pulse modulation control signal is coupled to adjust an amplitude and to modulate an RF source signal to generate the pulse RF signal having an envelope defined by the pulse segments of the pulse pattern.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/343,539, entitled RADIO FREQUENCY GENERATOR PROVIDING COMPLEX RFPULSE PATTERN, filed Jun. 9, 2021, now U.S. Pat. No. 11,328,902, issuedMay 10, 2022, which is incorporated herein by reference for allpurposes.

FIELD OF THE INVENTION

The invention relates to a radio frequency (RF) generator and, inparticular, to an RF generator capable of generating complex pulsepatterns as the RF output signal using simple circuitry.

BACKGROUND OF THE INVENTION

A radio frequency (RF) generator or RF power supply is an industrialequipment used for supplying RF energy to a load device. RF generatorsare commonly used in the semiconductor industry, such as in plasmasemiconductor equipment for generating plasma for manufacturing siliconwafers. A typical RF system may include an RF generator and an impedancematch network driving a load, such as a plasma chamber. The RF powergenerated by the RF generator are precisely controlled so as to realizethe desired process conditions. In semiconductor applications, the RFgenerator may generate a continuous wave (CW) signal or apulse-modulated signal. A pulse-modulated RF generator applies the RFsignal by pulsing the RF signal to the load.

More specifically, modern plasma semiconductor processes often use RFenergy that is pulsed. Pulsed plasmas can result in a higher etchingrate, better uniformity, and less structural, electrical or radiation(e.g. vacuum ultraviolet) damage. Pulsed plasmas can also ameliorateunwanted artifacts in etched micro-features such as notching, bowing,micro-trenching and aspect ratio dependent etching. As such, pulsedplasmas may be indispensable in etching of the next generation ofmicrodevices with a characteristic feature size in the sub-10 nm regime.

Pulsing requirements for RF generators driving plasma processes haveevolved from simple on/off output power pulsing to more complex multiplelevels of pulsing, each output power level with different timingrequirements. These more complex requirements demand more complexcircuits to provide the pulsing signals to modulate RF power output.Current solutions for providing pulsing signal include using a timingcircuit for each pulse power level, where such implementation limits thecomplexity of the RF pulse signal modulation that can be realized. Forexample, in the conventional solution, a need for three-level RF signalpulsing requires typically 4-6 timing circuits to develop the pulsepattern. Conventional pulse timing control solutions are not practicalwhen demands for greater process control call for large number of pulselevels, such as 10 or 100.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a schematic diagram of an RF system in which an RF generatoris incorporated in some examples.

FIG. 2 is a schematic diagram of an RF generator incorporating a pulsegenerator circuit in embodiments of the present disclosure.

FIG. 3 is a schematic diagram of an RF generator incorporating a pulsegenerator circuit in embodiments of the present disclosure.

FIG. 4 , which includes FIGS. 4(a) and 4(b), illustrates theconfiguration of the digital memory in the pulse generator circuit inembodiments of the present disclosure.

FIG. 5 , which includes FIGS. 5(a) and 5(b), includes exemplarypulse-modulated RF signal waveforms which can be generated by the RFgenerator in embodiments of the present disclosure.

FIG. 6 is a flowchart illustrating a method for generating apulse-modulated RF signal in an RF generator in embodiments of thepresent disclosure.

DETAILED DESCRIPTION

According to embodiments of the present disclosure, a radio frequency(RF) generator incorporates a pulse generator circuit to generatecomplex and arbitrary pulse modulation of an RF signal. In someembodiments, the pulse generator circuit includes a divide-by-n timer incommunication with a digital memory storage storing in a set of memorylocations the specifications for the desired pulse modulation. The pulsegenerator circuit generates a pulse modulation control signal definingan envelope for the pulse-modulated RF output signal. The shape of theenvelope of the pulse-modulated RF output signal can have complex forms,as specified by the specifications stored in the digital memory storage.In particular, the pulse generator circuit of the present disclosureenables the RF generator to deliver a pulse-modulated RF output signalhaving any pattern shape. Providing complex patterns of RF powerdelivery lead to new level of process control in RF-driven semiconductorequipment.

The pulse generator circuit of the present disclosure enables the RFgenerator to generate pulse-modulated RF signal with high level of RFenvelope complexity, a complexity level not readily achievable usingconventional RF pulse generation methods. In particular, the pulsegenerator circuit of the present disclosure does not require multitudeof timing circuits. For example, conventional RF pulse generationmethods often require one timing circuit for each desired pulse level.The pulse generator circuit of the present disclosure is simple toimplement and is cost effective to construct while providing greaterflexibility and improved performance as compared to conventional RFpulse generation methods.

FIG. 1 is a schematic diagram of an RF system in which an RF generatoris incorporated in some examples. Referring to FIG. 1 , an RF system 1is provisioned to supply an RF signal 8 to deliver RF power to a load 6.For example, the load 6 can be a semiconductor equipment, such as aplasma semiconductor equipment. The RF signal 8 can be applied togenerate the plasma in a plasma tool, such as for etching asemiconductor component. The RF system 1 includes an RF generator 2generating the RF signal 8 having a predetermined RF frequency. In someexamples, the RF signal 8 can be a continuous wave, such as a sinusoidalwaveform, where the amplitude and/or frequency of the sinusoidalwaveform can be varied to vary the output power delivered to the load 6.

In other examples, the RF signal 8 can be a burst signal or apulse-modulated RF signal, that is, the RF signal is provided in burstsof a sinusoidal signal of different pulse widths. In the presentdescription, a pulse-modulated RF signal, also referred to as a “pulseRF signal,” refers to a burst RF signal or a modulated RF signal. Inother words, a pulse RF signal is an RF sinusoidal signal that ismodulated by a pulse modulation control signal which defines an envelopefor the modulated sinusoidal signal. In some examples, the RF sinusoidalsignal is provided at a constant frequency and amplitude but the powerdelivery to the load is varied by varying the pulse modulation controlsignal.

The RF signal 8 generated by the RF generator 2 is provided to animpedance matching network 4 which generates an impedance matched RFsignal 9 to provide to the load 6. In particular, the impedance matchingnetwork 4 operates to maximize the power provided to the load 6 andminimize the reflected power back to the RF generator. The impedancematching network 4 seeks to adjust the input impedance of the matchingnetwork to match the characteristics impedance of the transmission lineconnecting the RF generator 2 to the matching network 4. As a result,the impedance matching network 4 modifies the RF signal 8, such as thephase of the RF signal, to generate the impedance matched RF signal 9.

In the present example, the RF generator 2 receives an input signal “RFPower Target” 7 a specifying the RF power level or levels to bedelivered. In the case the RF generator 2 provides a pulse RF signal,the RF generator 2 may further receives a second input signal “RF PulseTarget” 7 b specifying the pulse width or the pulse duration of thepulse RF signal. The RF generator 2 generates the pulse RF signal 8 inaccordance with the power level(s) and pulse width indicated by the RFPower Target 7 a and the RF Pulse Target 7 b. Furthermore, the RFgenerator 2 implements RF signal level control by measuring or samplingthe RF signal at its output terminal. The sampled RF signals 3, whichusually includes the forward RF signal and the reflected RF signal, isfed back to the RF generator 2 to form the control loop for adjustingthe level or the amplitude of the RF signal. Meanwhile, the impedancematching network 4 samples the pulse RF signal 8 and the sampled RFsignal 5 is used to adjust the input impedance of the matching networkto match the characteristics impedance of the transmission lineconnecting the RF generator 2 to the matching network 4, as describedabove.

Embodiments of the present disclosure describe an RF generatorincorporating a pulse generator circuit for controlling the pulsemodulation of the output RF signal.

FIG. 2 is a schematic diagram of an RF generator incorporating a pulsegenerator circuit in embodiments of the present disclosure. Referring toFIG. 2 , an RF generator 10 (also referred to as an “RF power supply”)generates an RF signal from an RF signal source 22 and provides the RFsignal an output terminal 36 for driving a load, usually via animpedance matching network. The RF generator 10 receives an input signalRF Power Target (node 12) and an input signal RF Pulse Target (node 14)specifying the desired power level(s) and the desired pulse width orpulse duration for the RF signal to be generated. In the presentembodiment, the RF signal thus generated is a pulse-modulated RF signalor a pulse RF signal. In embodiments of the present disclosure, the RFPower Target signal 12 can include one or more RF power setpoints andthe RF Pulse Target signal 14 can include one or more pulse durationsetpoints.

The RF generator 10 includes a controller 40 forming a feedback controlloop in the RF generator to regulate the power level or amplitude of theRF signal. In particular, the controller 40 generates a modulationcontrol signal 49 to control the power level of the RF signal inresponse to the feedback control loop. The controller 40 is further incommunication with a pulse generator circuit 50 to generate themodulation control signal 49 to control the pulse envelop of the outputRF signal to provide the desired pulse modulation pattern. As a result,the controller 40 generates the output RF signal (node 36) having anamplitude indicative of the RF Power Target (node 12) and having a pulseenvelope defined by the RF Pulse Target (node 14). The RF generator 10may include other circuits and components not shown to support thefunctionality of the RF generator. Other circuits and components of theRF generator 10 are omitted in FIG. 2 to simplify the discussion.

More specifically, in RF generator 10, an oscillator 22 serves as the RFsignal source and provides an RF source signal of a predetermined RFfrequency as a function of an RF clock CLK1. In one example, theoscillator 22 generates the RF source signal being a fixed-amplitudesine wave at an RF frequency. The RF source signal is modulated by asignal modulator 26. In embodiments of the present disclosure, thesignal modulator 26 is configured to gate or modulate the RF sourcesignal to generate a pulse-modulated RF signal as the output RF signal.The signal modulator 26 is coupled to adjust the signal level or theamplitude of the RF source signal as well as to pulse modulate the RFsource signal in response to the modulation control signal 49 from thecontroller 40. The modulated RF signal generated by the signal modulator26 may be amplified by a power amplifier 30 by a predeterminedamplification factor. The power amplifier 30 amplifies the power of theRF signal to realize a desired signal amplitude for the output RFsignal. The RF signal thus generated is provided on the output terminal36 and can be transmitted to the load on a transmission line, via animpedance matching network.

To realize feedback control, the RF signal is provided to the outputterminal 36 through directional couplers 31. The directional couplers 31attenuate and extract respective forward RF power (node 33) andreflected RF power (node 35) at the output terminal 36 where the sampledsignals are used in the feedback control loop to adjust the amplitudelevel of the output RF signal. In some examples, a directional couplersamples a small fraction of the output power (the forward RF signal orthe reflected RF signal) and diverts the sample to the controller 40.The controller 40 processes the forward and reflected RF signal samplesto generate measured signal level values. The controller 40 thengenerates an error signal indicative of a difference between themeasured signal level values of the RF signal and a reference signallevel. In some embodiments, the reference signal level is indicated bythe RF Power Target (node 12) indicating the desired RF power level orlevels for the output RF signal. The controller 40 generates themodulation control signal 49 in response to the error signal to controlthe amplitude of the output RF signal through the signal modulator 26.As thus configured, the feedback control loop is formed in the RFgenerator 10 to enable the controller 40 to continuously monitor andcontrol the output power level of the RF signal.

In operation, the controller 40 receives a pulse modulation controlsignal 58 from the pulse generator circuit 50. The pulse generatorcircuit 50 receives the RF Power Target (node 12) and the RF PulseTarget (node 14). The pulse generator circuit 50 generates the pulsemodulation control signal 58 indicative of the desired power level asspecified by the RF Power Target signal 12 and the desired pulse widthas specified by the RF Pulse Target signal 14. In one embodiment, thepulse modulation control signal 58 is a signal having a signal levelindicative of the desired power level and having a signal pulse widthindicative of the desired pulse width. The pulse modulation controlsignal 58 is provided to the controller 40 as a reference signal levelto use for controlling or adjusting the amplitude of the output RFsignal in the feedback control loop. Furthermore, the signal pulse widthof the pulse modulation control signal 58 is provided to the controller40 to indicate the duration in time that the pulse modulation is to beapplied to the RF signal to generate the pulse-modulated RF signal. Inparticular, the combination of the signal level and the signal pulsewidth of the pulse modulation control signal 58 specifies a shape or anenvelope for the pulse-modulated RF signal. In other embodiments, thepulse modulation control signal 58 can be provided as two signals, onesignal indicating the power level and another signal indicating thepulse duration. The exact structure of the pulse modulation controlsignal 58 is not critical to the practice of the present disclosure.

The controller 40 compares the forward RF Power signal 33 to the pulsemodulation control signal 58 to create an error signal that drives themodulation control signal 49. As a result, the modulation control signal49 drives the signal modulator 26 to modify the amplitude and to controlthe modulation of the RF source signal 22 to generate the output RFsignal with the desired signal amplitude (or RF power level) and thedesired pulse modulation pattern. In some examples, the signal modulator26 can be a multiplier combining the RF source signal and the modulationcontrol signal 49 provided by the controller 40.

In the present embodiment, the RF signal thus generated is apulse-modulated RF signal. In the present description, a pulse-modulatedRF signal, also referred to as a pulse RF signal, refers to an RF signalof a given RF frequency having an On period where the RF signal isprovided at an output terminal and an Off period where no RF signal isprovided. That is, the RF signal of the given RF frequency is providedonly during the On period. The On period and the Off period may berepeated and the pulsed RF signal may have the same or different pulsewidths for each pulse of the RF signal. Furthermore, in the presentdescription, the pulse-modulated RF signal may have various pulsepattern during the On period where the pulse pattern is specified by theRF Power Target signal 12 and the RF Pulse Target signal 14. Forexample, the pulse pattern may include two or more power levels, each ofthe same or different durations. The pulse generator circuit 50 in theRF generator 10 of the present disclosure is configured to generate apulse-modulated RF signal having any desired modulation pattern foroptimal RF power delivery to the load.

FIG. 3 is a schematic diagram of an RF generator incorporating a pulsegenerator circuit in embodiments of the present disclosure. Referring toFIG. 3 , an RF generator 100 (also referred to as an “RF power supply”)includes an RF circuit 20, a controller 40 and a pulse generator circuit50. The RF generator 100 generates an RF signal from an RF signal source22 and provides the RF signal an output terminal 36 for driving a load,usually via an impedance matching network. The RF generator 100 mayinclude other circuits and components not shown to support thefunctionality of the RF generator. Other circuits and components of theRF generator 100 are omitted in FIG. 3 to simplify the discussion.

In RF circuit 20, an oscillator 22 generates the RF source signal of apredetermined RF frequency as a function of an RF clock CLK1. In oneexample, the oscillator 22 generates the RF source signal being afixed-amplitude sine wave at the RF frequency. The RF source signal maybe amplified by a driver 24. The RF source signal is then modulated by asignal modulator 26. The signal modulator 26 is configured to gate ormodulate the RF source signal to generate a pulse-modulated RF signal asthe output RF signal. The signal modulator 26 is coupled to adjust thesignal level or the amplitude of the RF source signal as well as topulse modulate the RF source signal in response to a modulation controlsignal 49 from the controller 40. The modulated RF signal may be furtheramplified by a driver 28 and a power amplifier 30. For example, thepower amplifier 30 amplifies the power of the RF signal outputted fromthe signal modulator 26 by a predetermined amplification factor. Thepower amplifier 30 amplifies the power of the RF signal to realize adesired signal amplitude for the output RF signal. The RF signal thusgenerated is provided on the output terminal 36 and can be transmittedto the load on a transmission line to the load, via an impedancematching network.

To realize feedback control, the RF signal is provided to the outputterminal 36 of the RF circuit 20 through a pair 31 of directionalcouplers 32, 34. The directional couplers 32, 34 attenuate and extractrespective forward power (node 33) and reflected power (node 35) at theoutput terminal 36 where the sampled signals are used for monitoring ofthe output level of the RF generator 100. In other words, eachdirectional coupler samples a small fraction of the output power (theforward RF signal or the reflected RF signal) and diverts the sample tothe controller 40.

In the present embodiment, in the controller 40, samples of the forwardRF signal outputted by the directional coupler 32 is provided to ananalog-to-digital converter (ADC) 42 to be converted to digital datasamples. Similarly, samples of the reflected RF signal outputted by thedirectional coupler 34 is provided to an analog-to-digital converter(ADC) 44 to be converted to digital data samples. The digital datasamples of the forward and reflected RF signals are the processed by anerror processor 45. The error processor 45 generates an error signal(node 46) indicative of a difference between the measured signal levelvalues of the RF signal, as indicated by the digital data samples, and areference signal level. In embodiments of the present disclosure, thereference signal level is indicative by the pulse modulation controlsignal 58 generated by the pulse generator circuit 50, as will beexplained in more detail below.

The controller 40 includes a control modulator 47 which combines theerror signal 46 and the pulse modulation control signal 58 to generatesa modulation control signal 49. In some embodiments, the modulationcontrol signal 49 is a digital signal and is converted to analog form bya digital-to-analog converter 48. The converted modulation controlsignal is then provided to the signal modulator 26 to control themodulation of the RF source signal 22 and also to modify the level oramplitude of the RF source signal 22 to generate the output RF signal onoutput terminal 36 with the desired pulse modulation and the desiredsignal amplitude. As thus configured, a feedback control loop is formedin the RF generator 100 to enable the controller 40 to continuouslymonitor and control the output power or output level of the RF signal.The controller 40 generates the pulse RF signal (node 36) having anamplitude indicative of the RF Power Target (node 12) and having a pulseenvelope defined by the RF Pulse Target (node 14). In some embodiments,the signal modulator 26 is a multiplier combining the RF source signal22 and the modulation control signal 49 provided by the controller 40.

In the present description, the RF signal thus generated is apulse-modulated RF signal. The pulse-modulated RF signal can have anypulse shape or pulse envelop as defined by the RF Power Target and theRF Pulse Target. The RF generator 100 includes the pulse generatorcircuit 50 to generate the pulse modulation control signal 58 containinginformation for the desired signal level and desired pulse duration forthe pulse-modulated RF signal, which in combination, specify a shape oran envelope for the pulse-modulated RF signal.

In some embodiments, the pulse generator circuit 50 includes a digitalmemory 52 including a series of memory locations, each memory locationstoring a power level and a pulse duration for a segment of the pulse RFsignal to be generated. The pulse generator circuit 50 also includes adivide-by-N timer 54 in communication with the digital memory 52 togenerate the pulse modulation control signal 58 for the controller 40. Alogic circuit 56 control the operation of the divide-by-N timer 54 andthe digital memory 52.

In some embodiments, the digital memory 52 is an array of randomlyaccessible memory cells, such as DRAM memory cells or SRAM memory cells.In some embodiments, the digital memory 52 includes a given number ofmemory locations to support the programming of any pulse patterns forthe pulse RF signal, including complex pulse patterns.

In some embodiments, the divide-by-N timer 54, also referred to as adivide-by-N clock or divide-by-N counter, is a circuit for dividing areference clock signal. For example, the divide-by-N timer 54 receives areference clock signal 53 having a clock frequency F=1/T, where Tdenotes the clock period T of the reference clock signal. Thedivide-by-N timer 54 generates an output clock signal (also referred toas a “timing signal”) which is reset at the Nth clock pulse of thereference clock signal. In this way, the divide-by-N timer is used tospecify a given time duration with reference to the frequency or clockperiod of the reference clock signal.

More specifically, the divide-by-N timer generates an output clocksignal having a frequency being F divided by 2^(N) and a correspondingperiod being T multiplied by 2N. For example, for N=1, the divide-by-NTimer 54 generates an output clock signal having a frequency of ½T and aperiod of 2T. For N=2, the divide-by-N Timer 54 generates an outputclock signal having a frequency of ¼T and a period of 4T. In someembodiments, the divide-by-N timer 54 is implemented as one or more Dflip-flops. In the case of two or more D flip-flops, the D flip-flopsare connected in a serial chain.

In embodiments of the present disclosure, the divide-by-N timer 54 andthe digital memory 52 operate under the control of the logic circuit 56to generate the pulse modulation control signal 58 in response to the RFPower Target 12 and the RF Pulse Target 14. In particular, the RF PowerTarget signal 12 and the RF Pulse Target signal 14 provide setpointswhich together specify the pulse pattern to be applied to thepulse-modulated RF signal. In the present embodiment, each pulse patternis divided into pulse segments (or “segments”) where each pulse segmentis a portion or an interval of the pulse pattern having the same powerlevel.

In digital memory 52, each digital memory location stores dataassociated with a pulse segment or a pulse interval of the desired pulsepattern as programmed by the RF Power Target signal 12 and the RF PulseTarget signal 14. In some embodiments, each digital memory locationstores two values for each pulse interval: (1) the pulse interval'soutput power level and (2) the pulse interval's duration in time. Thepower level number stored for each pulse interval is used by the pulsegenerator circuit 50 to set the signal level of the pulse modulationcontrol signal 58. The signal level of the pulse modulation controlsignal 58 is provided to the controller 40 to adjust the power level ofthe RF signal in the feedback control loop. In the present embodiment,the signal level of the pulse modulation control signal 58 is providedto the error processor 45 of controller 40.

Meanwhile, the interval duration number stored for each pulse intervalis provided to the divide-by-N timer 54 to count the clock pulses of thereference clock signal based on the interval duration number. In otherwords, the interval duration number is used to set the Nth clock pulseof the reference clock signal 53 at which point the interval durationexpires and the output clock signal (or the timing signal) of thedivide-by-N timer 54 reset. The timing signal of the divide-by-N timer54 is used to set the pulse width or pulse duration of the pulsemodulation control signal 58 which is used to control the pulse envelopeof the RF signal. The pulse modulation control signal 58 thus generated,including a signal level indicative of the desired power level and asignal pulse width indicative of the desired pulse duration, is providedto the controller 40.

In operation, when the timer reaches the programmed time interval,indicating the pulse segment has completed, the digital memory 52advances digital memory location to the next pulse interval. Thesequence is continued until a memory location is reached that containsan “end power level” or an “end duration value.” The end power level orend duration value points the operation back to the beginning memorylocation. As thus, configured, the pulse generator 50 can be programmedto generate pulse pattern of any complexity level. The complexity of apulse modulation pattern is only limited by the number of the digitalmemory locations provided in digital memory 52.

FIG. 4 , which includes FIGS. 4(a) and 4(b), illustrates theconfiguration of the digital memory in the pulse generator circuit inembodiments of the present disclosure. Referring to FIG. 4(a), a digitalmemory 52 in the pulse generator circuit 50 includes a series of digitalmemory locations 60 a to 60 n. In the present embodiment, each memorylocation 60 stores a pair of values specifying the power level and thetime duration of a pulse interval or a pulse segment of a pulse RFsignal pattern. Specifically, the output power level (e.g. in unit ofWatts) and the duration (e.g. in unit of micro-seconds) for a givenpulse interval is stored in each memory location 60. A series of memorylocations 60 a to 60 n stores a sequence of pulse intervals for defininga pulse pattern. The digital memory 52 operates by starting at abeginning memory location, such as memory location 60 a, andincrementing to each subsequent memory location until a memory locationwith an end power level or end duration value is reached. In that case,the digital memory 52 returns to the beginning memory location 60 a andthe sequence is repeated.

In one example, a simple On-Off pulse pattern requires the programmingof 3 memory locations. At a first memory location: the values (500, 10)are stored for a pulse interval having a power level of 500 watts and aduration of 10 μs (On period). At a second memory location, the values(0, 90) are stored for a pulse interval having 0 watts and a duration of90 μs (Off period). At a third memory location, the values (−1, 0) arestored to represent the end of the pulse sequence. In the presentexample, the power level of “−1” indicates the end power level and thetime duration of “0” indicates the end duration value. The pulse RFsignal specified by these three memory locations will be as follows. The‘On’ power in the first memory location is 500 watts and lasts for aduration of 10 μs. The second memory location holds the ‘Off’ power of 0watts for 90 μs. When the third memory location is reached, the end ofpulse sequence is indicated and the memory pointer is immediatelyreturned to the first memory location and the process repeats togenerate the pulse pattern. The pulse pattern thus generated has arepetition rate of 10 KHz and a duty cycle of 10%.

FIG. 4(b) depicts another example of a pulse pattern that can begenerated using the pulse generator circuit 50 in embodiments of thepresent disclosure. Referring to FIG. 4(b), the digital memory 52includes a number of memory locations 60 storing pairs of data valuesspecifying the power level and the time duration of a pulse interval. Ata memory location 60-1: the values (500, 10) are stored. At memorylocation 60-2, the values (300, 40) are stored. At memory location 60-3,the values (0, 90) are stored. At memory location 60-4, the values (−1,0) are stored to indicate the end of the pulse pattern sequence. Thepulse RF signal specified by these four memory locations is as followsand is also shown in FIG. 5(a). The ‘On’ power in the first memorylocation is 500 watts and lasts for a duration of 10 μs. The ‘On’ powerin the second memory location is 300 watts and lasts for a duration of40 μs. The third memory location holds the ‘Off’ power of 0 watts for 90μs. When the fourth memory location is reached, the memory pointer isreturned to the first memory location 60-1 and the pulse pattern repeatsby applying the values stored in each memory location in sequence fromthe first memory location 60-1 to the last memory location 60-4.

FIG. 5 , which includes FIGS. 5(a) and 5(b), includes exemplarypulse-modulated RF signal waveforms which can be generated by the pulsegenerator circuit of the RF generator in embodiments of the presentdisclosure. Referring to FIG. 5(a), a pulse-modulated RF signal 70includes a pulse pattern where the On-period has two different signallevels and with different pulse durations. In particular, thepulse-modulated RF signal 70 of FIG. 5(a) is specified by the power andduration values stored in the digital memory 52 in FIG. 4(b).

FIG. 5(b) illustrates another example of a complex pulse pattern of apulse RF signal which can be generated using the pulse generator circuitof the present disclosure. Referring to FIG. 5(b), the pulse RF signal72 includes multiple signal levels during the On-period, where eachsignal level has different durations. The pulse pattern of FIG. 5(b) canbe programmed using six memory locations in the digital memory of thepulse generator circuit.

The curves 70 and 72 in FIGS. 5(a) and 5(b) denote the pulse envelopesof the pulse-modulated RF signal. During each On-period, thepulse-modulated RF signal provides an RF signal 75 having predeterminedRF frequency and having an amplitude defined by the pulse pattern. Inthe present example, the RF signal 75 is a sinusoidal waveform at the RFfrequency. In the examples shown in FIGS. 5(a) and 5(b), the underlyingsinusoidal waveform of the RF signal 75 is modulated by the pulseenvelopes 72, 74 to generate the respective pulse-modulated RF signals.

The pulse generator circuit 50 of the present disclosure can beadvantageously applied to generate complex pulse pattern to use as thepulse RF signal, thereby enabling enhanced process control. Thesimplistic and ease of implementation of the pulse generator circuit ofthe present disclosure is not achievable by convention solutions.

FIG. 6 is a flowchart illustrating a method for generating apulse-modulated RF signal in an RF generator in embodiments of thepresent disclosure. Referring to FIG. 6 , a method 200 for generating apulse-modulated RF signal (or pulse RF signal) starts by generating anRF source signal of a first frequency (202). The method 200 thenmodulates the RF source signal in response to a control signal togenerate the pulse RF signal (204).

The method 200 receives input signals indicative of a pulse pattern tobe applied to the pulse RF signal (206). In particular, the pulsepattern defines a pulse envelope of the pulse RF signal. In someexamples, the input signals can be the RF Power Target and RF PulseTarget signals described above. The method 200 stores, in a series ofmemory locations, data values describing the pulse pattern specified bythe input signals (208). In some embodiments, each memory locationstores data including a power level and a duration value for arespective segment of the pulse pattern. The series of memory locationsinclude a last memory location storing an end power level or an endduration value.

The method 200 select a first memory location from the series of memorylocations (210). The method 200 retrieves the power level and theduration value from the selected memory location (212). The method 200generates a pulse modulation control signal having a signal levelindicative of the retrieved power level and a signal pulse widthindicative of the retrieved duration value. (214). The method 200provides signal level of the pulse modulation control signal as areference signal level for controlling the amplitude of the pulse RFsignal and provides the signal pulse width of the pulse modulationcontrol signal as a timing signal (216). The combination of thereference signal level and the timing signal defines the pulse envelopeof the pulse-modulated RF signal. The method 200 generates the controlsignal in response to the reference signal level and the timing signal(218). The method 200 modulates the RF source signal in response to thecontrol signal to generate the pulse RF signal having the pulse patternas the pulse envelope (220).

In some embodiments, when the timing signal indicates the duration foreach segment expires, the method 200 moves to the next memory locationand repeats the process until the method 200 reaches the last memorylocation with the end power level or the end duration value. In responseto reaching the last memory location, the method 200 returns to thefirst memory location and the process repeats to generate the pulse RFsignal having the desired pulse pattern.

In embodiments of the present disclosure, the pulse generator circuit 50described above may be embodied as a device, system, method or computerprogram product. Accordingly, aspects of this disclosure, generallyreferred to herein as circuits, modules, components or systems, may beembodied in hardware, in software (including firmware, residentsoftware, micro-code, etc.), or in any combination of software andhardware, including computer program products embodied in anon-transitory computer-readable medium having computer-readable programcode embodied thereon. In some embodiments, the pulse generator circuit50 is implemented as a system including a hardware processor and amemory coupled with the hardware processor where the processor isconfigured to execute instructions stored in the memory to implement thefunctions of generating the pulse modulation control signal in responseto the RF Power target signal and the RF Pulse target signal, asdescribed above. The instructions may be program code, software code orsoftware program residing in firmware and/or on computer useable mediumhaving control logic for enabling execution on the processor. Forexample, in some embodiments, the logic circuit 56 in the pulsegenerator circuit 50 may be a hardware processor in communication with amemory storing program code or instructions, the divide-by-N timer 54may be implemented in software or firmware stored in the memory, and thedigital memory 52 may be implemented using the embedded memory in thehardware processor. The hardware processor in the pulse generatorcircuit 50 executes program code or instructions stored in the memory toperform the operation of the divide-by-N timer to generate the pulsemodulation control signal.

In this detailed description, various embodiments or examples of thepresent invention may be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter, a computerprogram product embodied on a non-transitory computer readable storagemedium; and/or a processor, such as a hardware processor or a processordevice, configured to execute instructions stored on and/or provided bya memory coupled to the processor; and/or a series of programinstructions on a non-transitory computer-readable medium (e.g., acomputer-readable storage medium or a computer network where the programinstructions are sent over optical, electronic, or wirelesscommunication links). In general, the order of the steps of disclosedprocesses may be altered within the scope of the invention. Unlessstated otherwise, a component such as a processor or a memory describedas being configured to perform a task may be implemented as a generalcomponent that is temporarily configured to perform the task at a giventime or a specific component that is manufactured to perform the task.As used herein, the term ‘processor’ refers to one or more devices,circuits, and/or processing cores configured to process data, such ascomputer program instructions.

A detailed description of one or more embodiments of the invention isprovided above along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. Numerous modifications and variations within the scope ofthe present invention are possible. The scope of the invention islimited only by the claims and the invention encompasses numerousalternatives, modifications and equivalents. Numerous specific detailsare set forth in the description in order to provide a thoroughunderstanding of the invention. These details are provided for thepurpose of example and the invention may be practiced according to theclaims without some or all of these specific details. For the purpose ofclarity, technical material that is known in the technical fieldsrelated to the invention has not been described in detail so that theinvention is not unnecessarily obscured. The present invention isdefined by the appended claims.

The invention claimed is:
 1. A radio frequency generator providing apulse radio frequency (RF) signal, comprising: a pulse generator circuitconfigured to receive input signals indicative of a pulse patterncomprising pulse segments, the input signals defining power levels anddurations for the pulse segments, the pulse generator circuit generatinga pulse modulation control signal for each pulse segment responsive tothe input signals, the pulse modulation control signal being coupled toadjust an amplitude and to modulate an RF source signal to generate thepulse RF signal having an envelope defined by the pulse segments of thepulse pattern; a digital memory comprising a plurality of memorylocations, each memory location storing a power level and a durationvalue associated with a respective pulse segment of the pulse pattern,and a last memory location storing an end power level or an end durationvalue; and a divide-by-N timer receiving the duration value for arespective pulse segment from a respective memory location andgenerating a first signal indicative of the duration value of therespective pulse segment, wherein the pulse generator circuit providesthe stored power level from a respective memory location as a signallevel of the pulse modulation control signal and provides the firstsignal indicative of the duration value stored at the same memorylocation as a pulse width of the pulse modulation control signal, thepulse modulation control signal being provided to modulate the RF sourcesignal to generate the pulse RF signal having the envelope defined bythe pulse segments of the pulse pattern.
 2. The radio frequencygenerator of claim 1, further comprising: a radio frequency (RF) circuitcomprising an RF signal source providing the RF source signal having afirst frequency and a signal modulator generating the pulse RF signalhaving an On period where the RF signal is provided at an outputterminal and an Off period where no RF signal is provided; and a controlcircuit configured to sample the pulse RF signal at the output terminaland to generate a control signal responsive to at least the sampledpulse RF signal to modulate the RF signal at the radio frequencycircuit, wherein the pulse generator circuit provides the pulsemodulation control signal to the control circuit to generate the controlsignal to adjust the amplitude and to modulate the RF source signal togenerate the pulse RF signal having the envelope defined by the pulsesegments of the pulse pattern.
 3. The radio frequency generator of claim2, wherein the control circuit provides the control signal to the signalmodulator of the radio frequency circuit to control the amplitude andthe modulation of the RF source signal to generate the pulse RF signal.4. The radio frequency generator of claim 2, wherein control circuitfurther comprises: first and second analog-to-digital convertersconfigured to sample respective forward RF signal and reflected RFsignal at the output terminal and to generate digital samples of therespective forward and reflected RF signals; an error processorconfigured to compare a measured signal level value to a referencesignal level to generate an error signal indicative of a differencethereof, the measured signal level being derived from the digitalsamples of the respective forward and reflected RF signals and thereference signal level being the power level indicated by the pulsemodulation control signal provided by the pulse generator circuit; and acontrol modulator configured to generate the control signal in responseto the error signal and the pulse modulation control signal generated bythe pulse generator circuit, the pulse modulation control signalindicating the duration of each segment of the pulse pattern to beapplied to the pulse RF signal.
 5. The radio frequency generator ofclaim 2, further comprising: a digital-to-analog convert configured toconvert the control signal to an analog signal and to couple the analogsignal to control the signal modulator of the radio frequency circuit.6. The radio frequency generator of claim 2, wherein the pulse generatorcircuit comprises a hardware processor and a memory coupled to thehardware processor, wherein the memory is configured to provide theprocessor with instructions which when executed cause the processor to:receive the input signals indicative of the pulse pattern defining thepulse envelope of the pulse RF signal; store the data values definingpower levels and durations for segments of the pulse pattern; generatethe pulse modulation control signal for each segment responsive to thestored data values, the pulse modulation control signal being indicativeof the power level and the duration of each segment of the pulsepattern; and provide the pulse modulation control signal to the controlcircuit to generate the control signal to adjust an amplitude and tomodulate the RF source signal to generate the pulse RF signal having thepulse pattern as the pulse envelope.
 7. The radio frequency generator ofclaim 1, wherein the pulse generator circuit selects the memorylocations in the digital memory in sequence from a first memory locationto the last memory location, the pulse generator circuit generating thepulse modulation control signal using the duration value of eachselected memory location and the power level of the same selected memorylocation, the pulse generator circuit returning to the first memorylocation in response to selecting the last memory location.
 8. The radiofrequency generator of claim 1, wherein divide-by-N timer countsclocking pulses of a reference clock signal based on the duration valueand resetting the pulse width of the pulse modulation control signal atthe expiration of the duration value to indicate an end of therespective pulse segment.
 9. The radio frequency generator of claim 1,wherein the pulse pattern comprises a plurality of pulse segments, eachsegment having a different power level than at least one other segmentand each segment having a different duration than at least one othersegment.
 10. The radio frequency generator of claim 1 wherein thedigital memory comprises a plurality of randomly accessible memorycells.
 11. The radio frequency generator of claim 1, wherein thedivide-by-N timer comprises a plurality of D flip-flops connected in aserial chain.
 12. A method of generating a pulse radio frequency (RF)signal in an RF generator, comprising: receiving input signalsindicative of a pulse pattern comprising pulse segments to be applied toan RF source signal to generate the pulse RF signal having an envelopedefined by the pulse segments of the pulse pattern, the input signalsdefining a power level and a duration for each pulse segment; storing,in a series of memory locations, data values describing the pulsepattern specified by the input signals, each memory location storingdata comprising a power level and a duration value for a respectivesegment of the pulse pattern, the series of memory locations comprisinga last memory location storing an end power level or an end durationvalue, selecting a first memory location from the series of memorylocations; retrieving the power level and the duration value from theselected memory location; generating a pulse modulation control signalfor each pulse segment responsive to the input signals, comprisinggenerating the pulse modulation control signal having a signal levelindicative of the retrieved power level and a signal pulse widthindicative of the retrieved duration value; providing the signal levelof the pulse modulation control signal as a reference signal level forcontrolling the amplitude of the pulse RF signal; providing the signalpulse width of the pulse modulation control signal as a timing signal;and providing the pulse modulation control signal to adjust an amplitudeand to modulate the RF source signal to generate the pulse RF signalhaving an envelope defined by the pulse segments of the pulse pattern.13. The method of claim 12, further comprising: generating an RF sourcesignal of a first frequency; generating a control signal in response tothe pulse modulation control signal indicating a given power level and agiven duration for each pulse segment; and modulating the RF sourcesignal in response to the control signal to generate the pulse RF signalhaving the envelope defined by the pulse segments of the pulse pattern.14. The method of claim 13, further comprising: generating the controlsignal in response to the reference signal level and the timing signalassociated with the pulse modulation control signal.
 15. The method ofclaim 14, further comprising: selecting the memory location in theseries of memory locations in sequence from the first memory location tothe last memory location; for each selected memory location, repeatingretrieving the RF power level and the duration value to modulating theRF source signal to generate the pulse RF signal having the pulsepattern as the pulse envelope; and in response to the last memorylocation being selected, return to the first memory location andrepeating selecting the memory location at the first memory location.16. The method of claim 14, wherein generating a pulse modulationcontrol signal having a signal level indicative of the retrieved powerlevel and a signal pulse width indicative of the retrieved durationvalue comprises: generating, using a divide-by-N timer, the pulsemodulation control signal having a signal pulse width indicative of theduration value associated with the segment of the pulse pattern storedin the selected memory location.
 17. The method of claim 16, whereingenerating, using the divide-by-N timer, the pulse modulation controlsignal comprises: counting, based on the duration value, clocking pulsesof a reference clock signal; and resetting the timing signal at theexpiration of the duration value to indicate an end of the respectivesegment.
 18. The method of claim 13, further comprising: sampling aforward RF signal and a reflected RF signal relating to the pulse RFsignal to generate digital samples of the forward RF signal and thereflected RF signal; processing the selected digital samples to generatea measured signal level value; determining an error signal indicative ofa difference between the measured signal level value and the referencesignal level; generating the control signal in response to the errorsignal and the timing signal, the timing signal indicating the durationsof the segments of the pulse pattern to be applied to the pulsed RFsignal; and applying the control signal to modulate the RF source signalto generate the pulse RF signal having the pulse pattern.
 19. The methodof claim 12, wherein the pulse pattern comprises a plurality ofsegments, each segment having a different power level than at least oneother segment and each segment having a different duration than at leastone other segment.